def lone_sum(a, b, c):
  if a!=b and b!=c and a!=c:
    return (a+b+c)
  if a==b==c:
     return (0)
  if a!=b and b==c and a!=c:
      return (a)
  if a==b and b!=c and a!=c:
      return(c)
  if a==c and b!=a and b!=c:
      return(b)